Address book problem

Hello, I'm new to mac forums this being my first post.
I've had my imac for about a year now and am using OS X Lion.
I've just tried to send an email and I have noticed ALL of my contacts in the Address book have vanished. I'm the only one who uses this Mac. I tried to get them back via the Time machine, but you apparently can't edit or modify apps. I can't work out what has happened.
Any help would be grateful

That's strange though. The address book was upgraded with Lion and you should still have all your contacts in there as well, because anything you add in there is synced wirelessly via iCloud to your other devices and vice versa. What sync settings are you using ?